The present disclosure is directed to an engine valve actuator and, more particularly, the present disclosure is directed to an anti-lash mechanism for an engine valve actuator.
Many vehicles, such as, for example, automobiles, on highway trucks, or off highway trucks, typically include an internal combustion engine that provides power for the vehicle. A typical internal combustion engine includes a series of intake and exhaust valves that control the flow of gases to and from the combustion chambers of the engine. The engine may also include a valve actuation system, such as, for example, a cam driven valve actuation system to control the actuation timing of the engine valves.
The overall performance of the internal combustion engine may be improved by using a series of auxiliary valve actuators, such as, for example, hydraulically powered actuators, that actuate the engine valves to selectively implement variations on the conventional, cam-driven valve timing. For example, the auxiliary valve actuators may be used to actuate the exhaust valves of the engine to implement an xe2x80x9cengine brakingxe2x80x9d cycle. In an engine braking cycle, the auxiliary valve actuators open the exhaust valves of the engine when a piston associated with each combustion chamber is at or near a top-dead-center position of a compression stroke. This opening of the exhaust valves allows the air compressed by the piston in the combustion chamber during the compression stroke to escape from the combustion chamber through an exhaust passageway. In this manner, the pistons of the engine are selectively used as air compressors to absorb power instead of generating power in response to the combustion of fuel.
Because the auxiliary valve actuators are used only when the engine is experiencing selected operating conditions, the auxiliary valve actuators should avoid interfering with the operation of the cam driven valve actuation system when the engine is experiencing other operating conditions. The performance of the engine may be negatively impacted if, for example, the auxiliary valve actuators inadvertently opened the exhaust valves during the intake stroke of the pistons. This type of interference may occur if the auxiliary valve actuators do not account for changes in the size of engine components due to thermal expansion.
To prevent any such interference, the auxiliary valve actuators are typically separated from the exhaust valve assembly by a certain distance, which is commonly referred to as a xe2x80x9clash.xe2x80x9d The lash is a distance that separates the auxiliary valve actuators from the engine valve assembly. The lash may prevent inadvertent or unintentional opening of the engine valves by the auxiliary valve actuators when changes in temperature of the engine cause a change in size of the engine components.
However, the auxiliary valve actuators must take up the lash before engaging the engine valves to open the engine valves. This may result in the auxiliary valve actuators requiring additional fluid and/or additional time to open an associated engine valve. To obtain the best engine performance, the actuation timing of the engine valves should be controlled precisely. Accordingly, the system that controls the auxiliary valve actuators must account for the lash in each actuation of the associated engine valves.
An auxiliary valve actuator may include an anti-lash mechanism. For example, as illustrated in U.S. Pat. No. 4,898,128 to Meneely, an auxiliary valve actuator may include a relatively low force spring that biases the valve actuator into contact with the valve assembly. In this manner, the lash is removed and the auxiliary valve actuator remains in contact with the associated valve without impacting the performance of the engine under normal operating conditions. However, adding additional components to the auxiliary valve actuator increases the overall cost of the auxiliary actuator and may result in additional maintenance.
The engine valve actuator of the present disclosure solves one or more of the problems set forth above.
In one aspect, the present disclosure is directed to an engine valve actuator for an internal combustion engine that includes a housing having an opening. An adjustment member is disposed in the housing and defines a chamber. A piston is disposed in the opening of the housing and has a protrusion adapted to be received in the chamber of the adjustment member. The piston has a first position where the protrusion of the piston is disposed in the chamber and a portion of the piston contacts a corresponding portion of the adjustment member and a second position where the portion of the piston is separated from the corresponding portion of the adjustment member. A fluid passageway is adapted to provide pressurized fluid to the opening. The pressurized fluid acts on the piston to move the piston towards the second position to thereby allow pressurized fluid to enter the chamber to prevent the piston from returning to the first position. A push rod is operatively engaged with the piston and is adapted to engage and open the engine valve.
In another aspect, the present disclosure is directed to a method of an engine valve of an internal combustion engine. Pressurized fluid is provided to a housing defining an opening and including a chamber. The pressurized fluid is directed to the opening of the housing and against a piston having a protrusion engaged with the chamber. The pressurized fluid acts on the piston to move the piston from a first position where a portion of the piston engages a corresponding portion of the housing. The movement of the piston cause the engine valve to move to an open position and allows fluid to flow into the chamber. The engine valve is returned to a closed position. The movement of the engine valve acts to move the piston within the housing. The fluid in the chamber prevents the piston from returning to the first position.